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Talking agronomy with Maddy Vaughan: Many growers are dreading OSR harvest

At the time of writing, combines in the area are just starting to roll with winter barley yields looking to be fairly promising.

In contrast, many growers are dreading the start of oilseed rape harvest with many crops badly affected by last year’s poor establishment conditions and devastating cabbage stem flea beetle effects.

 

By the time this article is published many OSR crops will have been cut and an idea of the effect of the drought and CSFB on yield will be known.

 

Drilling of the 2020 oilseed rape crop will also no doubt have started for many, with growers keen to establish rape early to have an established crop by the middle of August.

 

Establishment

 

The summer of 2018 was particularly dry, and many establishment issues arose due to these dry conditions either preventing germination altogether, or the lack of moisture after germination and emergence preventing the crop from growing away from the CSFB onslaught.

 

While oilseed rape sowing advice as always centres around achieving good seedbeds so good seed-soil contact can be achieved, and drilling into moisture, many growers are keen to drill earlier this year.

 

Reasons behind this are sound with growers wanting to get seed into the ground so that if conditions are dry any moisture we do receive after sowing will be utilised by the crop and not lost during drilling.

 

Having an established plant by the main CSFB migration period which normally takes place towards the middle to end of August will also help the crop weather the CSFB attack.

 

This approach however is not without its limitations as it has been seen that larval infestation can be higher in crops which are drilled earlier.


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Talking agronomy with Maddy Vaughan: Better growing conditions should ease CSFB damage Talking agronomy with Maddy Vaughan: Better growing conditions should ease CSFB damage
Talking arable with Ian Matts: 'The sooner I can put this year’s OSR behind us the better' Talking arable with Ian Matts: 'The sooner I can put this year’s OSR behind us the better'

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Last year out on-farm, one of the most noticeable trends I observed was where the stubble had been left long there was less pest damage, and the OSR established well.

 

The reasons behind this are not clear and could be related to the dry conditions and moisture retention effect rather than direct pest deterrent of the long stubble.

 

However, this effect was seen elsewhere, and trials are being conducted to see if longer straw does reduce pressure and the reasons behind this.

 

Another method that has been shown to help decrease CSFB damage is to leave oilseed rape volunteers as long as possible to act as a trap crop attracting the pest away from drilled OSR crops.

 

Trials have shown this method can decrease adult attack in drilled OSR crops and decrease larval numbers too.

Weed burden

 

Leaving stubbles uncultivated in dry conditions also helps to decrease the weed seed burden.

 

When looking at shallow cultivations post-harvest it should be remembered that if we experience dry conditions immediate cultivation can lead to longer dormancy of weed seeds as dormancy is influenced by darkness and water stress.

 

Therefore, if dry conditions are experienced shallow cultivations should be delayed four weeks post-harvest.

 

Leaving cultivations also allows the predation of weed seeds on the surface, and with additional benefit of possibly reducing CSFB pressure in the drilled rape crops this approach could have numerous benefits.

Verticillium

 

Prior to combining, or indeed from just looking at the stubble, it is easy to see if the disease verticillium wilt is present in oilseed rape and is worth looking out for due to its detrimental effect on rape yield.

 

Symptoms can be seen in the OSR stubble, with the stems showing vertical grey lines with microsclerotia. These microsclerotia on the infected stubble produce soil inoculum as the stubble breaks down and can survive for a long time in the soil.

 

Therefore, identifying if verticillium wilt is present can help influence choices going forward such as lengthening oilseed rape rotations, growing a tolerant variety in the future or even if infestation is bad enough stopping growing oilseed rape in the field rotation.

 

The AHDB have been looking into whether significant differences exist between varieties to produce a verticillium disease rating on the recommended list.

 

They have found that variety reactions to verticillium infection are significantly and consistently different and so are getting closer to producing resistance ratings for this disease.

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